According to the Centers for Disease Control and Prevention, approximately 46.5 million surgical procedures are performed each year in the United States. Of those, approximately 5 million comprise gastrointestinal endoscopies, considered a more invasive medical procedure. Following these endoscopies, disinfection and sterilization are essential for ensuring that the medical and surgical instruments do not transmit infectious pathogens to subsequent patients.
Cleaning is described as the removal of visible soil (e.g., organic and inorganic material) from objects and surfaces and normally is accomplished manually or mechanically using water with detergents or enzymatic products. Thorough cleaning is essential before high-level disinfection and sterilization because inorganic and organic materials that remain on the surfaces of instruments interfere with the effectiveness of these processes. Also, if soiled materials dry or bake onto the instruments, the removal process becomes more difficult and the disinfection or sterilization process less effective or ineffective. Surgical instruments are typically presoaked or rinsed to prevent drying of blood and to soften or remove blood from the instruments.
Cleaning is done manually in use areas without mechanical units (e.g., ultrasonic cleaners or washer-disinfectors) or for fragile or difficult-to-clean instruments. With manual cleaning, the two essential components are friction and fluidics. Friction is accomplished, for example, by rubbing/scrubbing the soiled area with a brush. Fluidics (i.e., fluids under pressure) is used to remove soil and debris from internal channels after brushing and when the design does not allow passage of a brush through a channel. When a washer-disinfector is used, care is taken in loading instruments. For example, hinged instruments are opened fully to allow adequate contact with the detergent solution, stacking of instruments in washers is avoided, and instruments are disassembled as much as possible.
The most common types of mechanical or automatic cleaners are ultrasonic cleaners, washer-decontaminators, washer-disinfectors, and washer-sterilizers. Ultrasonic cleaning removes soil by cavitation and implosion in which waves of acoustic energy are propagated in aqueous solutions to disrupt the bonds that hold particulate matter to surfaces.
Disinfection describes a process that eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects. Disinfection is usually performed using liquid chemicals or wet pasteurization. High-level disinfection traditionally is defined as complete elimination of all microorganisms in or on an instrument, except for small numbers of bacterial spores. The Food and Drug Administration (FDA) definition of high-level disinfection is a sterilant used for a shorter contact time to achieve a 6-log10 kill of an appropriate Mycobacterium species. Cleaning followed by high-level disinfection should eliminate enough pathogens to prevent transmission of infection.
Laparoscopes and arthroscopes in the United States sometimes undergo only high-level disinfection between patients. As with flexible endoscopes, these devices can be difficult to clean and high-level disinfect or sterilize because of intricate device design (e.g., long narrow lumens, hinges). Meticulous cleaning must precede any high-level disinfection or sterilization process.
Sterilization describes a process that destroys or eliminates all forms of microbial life and is carried out in health-care facilities by physical or chemical methods. Steam under pressure, dry heat, ethylene oxide (EtO) gas, hydrogen peroxide gas plasma, and liquid chemicals are the principal sterilizing agents used in health-care facilities.
Factors that affect the efficacy of both disinfection and sterilization include prior cleaning of the object, organic and inorganic load present, type and level of microbial contamination, concentration of and exposure time to the germicide, physical nature of the object (e.g., crevices, hinges, and lumens), presence of biofilms, temperature and pH of the disinfection process, and in some cases, relative humidity of the sterilization process.
Decontamination removes pathogenic microorganisms from objects so they are safe to handle, use, or discard.
Rinsing endoscopes and flushing endoscope channels with sterile water, filtered water, or tap water will prevent adverse effects associated with disinfectant retained in the endoscope (e.g., disinfectant-induced colitis). Items can be rinsed and flushed using sterile water after high-level disinfection to prevent contamination with organisms in tap water, such as nontuberculous mycobacteria, Legionella, or gram-negative bacilli such as Pseudomonas. Alternatively, a tap water or filtered water (0.2 m filter) rinse should be followed by an alcohol rinse and forced air drying. Forced-air drying markedly reduces bacterial contamination of stored endoscopes, most likely by removing the wet environment favorable for bacterial growth. After rinsing, items should be dried and stored (e.g., packaged) in a manner that protects them from recontamination.
Physicians use endoscopes to diagnose and treat numerous medical disorders. Even though endoscopes represent a valuable diagnostic and therapeutic tool in modern medicine and the incidence of infection associated with their use reportedly is very low (about 1 in 1.8 million procedures), more healthcare-associated outbreaks have been linked to contaminated endoscopes than to any other medical device. To prevent the spread of health-care-associated infections, all heat-sensitive endoscopes (e.g., gastrointestinal endoscopes, bronchoscopes, nasopharyngoscopes) must be properly cleaned and, at a minimum, subjected to high-level disinfection after each use. High-level disinfection can be expected to destroy all microorganisms, although when high numbers of bacterial spores are present, a few spores might survive.
Because of the types of body cavities they enter, flexible endoscopes acquire high levels of microbial contamination (bioburden) during each use. For example, the bioburden found on flexible gastrointestinal endoscopes after use has ranged from 105 colony forming units (CFU)/mL to 1010 CFU/mL, with the highest levels found in the suction channels. The average load on bronchoscopes before cleaning was 6.4×104 CFU/ml. Cleaning reduces the level of microbial contamination by 4-6 log10. Using human immunovirus (HIV)-contaminated endoscopes, several investigators have shown that cleaning completely eliminates the microbial contamination on the scopes. Similarly, other investigators found that EtO sterilization or soaking in 2% glutaraldehyde for 20 minutes was effective only when the device first was properly cleaned.
The FDA maintains a list of cleared liquid chemical sterilants and high-level disinfectants that can be used to reprocess heat-sensitive medical devices, such as flexible endoscopes. At this time, the FDA-cleared and marketed formulations include: ≥2.4% glutaraldehyde, 0.55% ortho-phthalaldehyde (OPA), 0.95% glutaraldehyde with 1.64% phenol/phenate, 7.35% hydrogen peroxide with 0.23% peracetic acid, 1.0% hydrogen peroxide with 0.08% peracetic acid, and 7.5% hydrogen peroxide. These products have excellent antimicrobial activity; however, some oxidizing chemicals (e.g., 7.5% hydrogen peroxide and 1.0% hydrogen peroxide with 0.08% peracetic acid) reportedly have caused cosmetic and functional damage to endoscopes. EtO sterilization of flexible endoscopes is infrequent because it requires a lengthy processing and aeration time (e.g., 12 hours) and is a potential hazard to staff and patients. The two products most commonly used for reprocessing endoscopes in the United States are glutaraldehyde and an automated, liquid chemical sterilization process that uses peracetic acid. The American Society for Gastrointestinal Endoscopy (ASGE) recommends glutaraldehyde solutions that do not contain surfactants because the soapy residues of surfactants are difficult to remove during rinsing. Ortho-phthalaldehyde has begun to replace glutaraldehyde in many health-care facilities because it has several potential advantages over glutaraldehyde. Ortho-phthalaldehyde is not known to irritate the eyes and nasal passages, does not require activation or exposure monitoring, and has a 12-minute high-level disinfection claim in the United States. Disinfectants that are not FDA-cleared and should not be used for reprocessing endoscopes include iodophors, chlorine solutions, alcohols, quaternary ammonium compounds, and phenolics. These solutions might still be in use outside the United States, but their use is discouraged because of lack of proven efficacy against all microorganisms or materials incompatibility.
Flexible endoscopes are particularly difficult to disinfect and easy to damage because of their intricate design and delicate materials. Meticulous cleaning must precede any sterilization or high-level disinfection of these instruments. Failure to perform good cleaning can result in sterilization or disinfection failure and outbreaks of infection can occur. Several studies have demonstrated the importance of cleaning in experimental studies with the duck hepatitis B virus (HBV), HIV, and Helicobacter pylori. 
An examination of health-care-associated infections related only to endoscopes through July 1992 found 281 infections transmitted by gastrointestinal endoscopy and 96 transmitted by bronchoscopy. The clinical spectrum ranged from asymptomatic colonization to death. Salmonella species and Pseudomonas aeruginosa repeatedly were identified as causative agents of infections transmitted by gastrointestinal endoscopy, and M. tuberculosis, atypical mycobacteria, and P. aeruginosa were the most common causes of infections transmitted by bronchoscopy. Major reasons for transmission were inadequate cleaning, improper selection of a disinfecting agent, failure to follow recommended cleaning and disinfection procedures, and flaws in endoscope design or automated endoscope reprocessors. Failure to follow established guidelines has continued to result in infections associated with gastrointestinal endoscopes and bronchoscopes. One multistate investigation found that 23.9% of the bacterial cultures from the internal channels of 71 gastrointestinal endoscopes grew >100,000 colonies of bacteria after completion of all disinfection and sterilization procedures and before use on the next patient.
Automated endoscope reprocessors (AER) offer several advantages over manual reprocessing. AERs automate and standardize several important reprocessing steps, reduce the likelihood that an essential reprocessing step will be skipped, and reduce personnel exposure to high-level disinfectants or chemical sterilants. Failure of AERs has been linked to outbreaks of infections or colonization, and the AER water filtration system might not be able to reliably provide “sterile” or bacteria-free rinse water. Establishment of correct connectors between the AER and the device is critical to ensure complete flow of disinfectants and rinse water. In addition, some endoscopes, such as the duodenoscopes (e.g., for endoscopic retrograde cholangiopancreatography [ERCP]), contain features (e.g., elevator-wire channel) that require a flushing pressure that is not achieved by most AERs and must be reprocessed manually using a 2- to 5-mL syringe, until new duodenoscopes equipped with a wider elevator-channel that AERs can reliably reprocess become available. Outbreaks involving removable endoscope parts, such as suction valves and endoscopic accessories designed to be inserted through flexible endoscopes, such as biopsy forceps, emphasize the importance of cleaning to remove all foreign matter before high-level disinfection or sterilization. Some types of valves are now available as single-use, disposable products (e.g., bronchoscope valves) or steam sterilizable products (e.g., gastrointestinal endoscope valves).
AERs need further development and redesign, as do endoscopes, so that they do not represent a potential source of infectious agents. Endoscopes employing disposable components (e.g., protective barrier devices or sheaths) might provide an alternative to conventional liquid chemical high-level disinfection/sterilization. Another new technology is a swallowable camera-in-a-capsule that travels through the digestive tract and transmits color pictures of the small intestine to a receiver worn outside the body. This capsule currently does not replace colonoscopies.
In general, endoscope disinfection or sterilization with a liquid chemical sterilant involves five steps after leak testing:                1. Clean: mechanically clean internal and external surfaces, including brushing internal channels and flushing each internal channel with water and a detergent or enzymatic cleaners (leak testing is recommended for endoscopes before immersion).        2. Disinfect: immerse endoscope in high-level disinfectant (or chemical sterilant) and perfuse (eliminates air pockets and ensures contact of the germicide with the internal channels) disinfectant into all accessible channels, such as the suction/biopsy channel and air/water channel and expose for a time recommended for specific products.        3. Rinse: rinse the endoscope and all channels with sterile water, filtered water (commonly used with AERs) or tap water (i.e., high-quality potable water that meets federal clean water standards at the point of use).        4. Dry: rinse the insertion tube and inner channels with alcohol, and dry with forced air after disinfection and before storage.        5. Store: store the endoscope in a way that prevents recontamination and promotes drying.        
Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) are important health-care-associated agents. Some antiseptics and disinfectants have been known to be somewhat less inhibitory to Staphylococcus aureus strains that contain a plasmid-carrying gene encoding resistance to the antibiotic gentamicin. For example, gentamicin resistance has been shown to also encode reduced susceptibility to propamidine, quaternary ammonium compounds, and ethidium bromide, and MRSA strains have been found to be less susceptible than methicillin-sensitive Staphylococcus aureus (MSSA) strains to chlorhexidine, propamidine, and the quaternary ammonium compound cetrimide. In other studies, MRSA and MSSA strains have been equally sensitive to phenols and chlorhexidine, but MRSA strains were slightly more tolerant to quaternary ammonium compounds. Two gene families (qacCD [now referred to as smr] and qacAB) are involved in providing protection against agents that are components of disinfectant formulations such as quaternary ammonium compounds. Staphylococci have been proposed to evade destruction because the protein specified by the qacA determinant is a cytoplasmic-membrane-associated protein involved in an efflux system that actively reduces intracellular accumulation of toxicants, such as quaternary ammonium compounds, to intracellular targets.
A study that evaluated the efficacy of selected cleaning methods (e.g., quaternary ammonium cation [QUAT]-sprayed cloth, and QUAT-immersed cloth) for eliminating VRE found that currently used disinfection processes most likely are highly effective in eliminating VRE. However, surface disinfection must involve contact with all contaminated surfaces.
Organic matter in the form of serum, blood, pus, fecal, or lubricant material can interfere with the antimicrobial activity of disinfectants in at least two ways. Most commonly, interference occurs by a chemical reaction between the germicide and the organic matter resulting in a complex that is less germicidal or nongermicidal, leaving less of the active germicide available for attacking microorganisms. Chlorine and iodine disinfectants, in particular, are prone to such interaction. Alternatively, organic material can protect microorganisms from attack by acting as a physical barrier.
All lumens and channels of endoscopic instruments must contact the disinfectant. Air pockets interfere with the disinfection process, and items that float on the disinfectant will not be disinfected. The disinfectant must be introduced reliably into the internal channels of the device. The exact times for disinfecting medical items are somewhat elusive because of the effect of the aforementioned factors on disinfection efficacy. Certain contact times have proved reliable, but, in general, longer contact times are more effective than shorter contact times.
Microorganisms may be protected from disinfectants by the production of thick masses of cells and extracellular materials, or biofilms.
Of all the methods available for sterilization, moist heat in the form of saturated steam under pressure is the most widely used and the most dependable. Steam sterilization is nontoxic, inexpensive, rapidly microbicidal, sporicidal, and rapidly heats and penetrates fabrics. Like all sterilization processes, steam sterilization has some deleterious effects on some materials, including corrosion and combustion of lubricants associated with dental handpieces, reduction in ability to transmit light associated with laryngoscopes, and increased hardening time (5.6 fold) with plaster-cast.
The basic principle of steam sterilization, as accomplished in an autoclave, is to expose each item to direct steam contact at the required temperature and pressure for the specified time. Thus, there are four parameters of steam sterilization: steam, pressure, temperature, and time. The ideal steam for sterilization is dry saturated steam and entrained water (dryness fraction ≥97%). Pressure serves as a means to obtain the high temperatures necessary to quickly kill microorganisms. Specific temperatures must be obtained to ensure the microbicidal activity. The two common steam-sterilizing temperatures are 121° C. (250° F.) and 132° C. (270° F.). These temperatures (and other high temperatures) must be maintained for a minimal time to kill microorganisms. Recognized minimum exposure periods for sterilization of wrapped healthcare supplies are 30 minutes at 121° C. (250° F.) in a gravity displacement sterilizer or 4 minutes at 132° C. (270° C.) in a prevacuum sterilizer. At constant temperatures, sterilization times vary depending on the type of item (e.g., metal versus rubber, plastic, items with lumens), whether the item is wrapped or unwrapped, and the sterilizer type.
The two basic types of steam sterilizers (autoclaves) are the gravity displacement autoclave and the high-speed prevacuum sterilizer.
Another design in steam sterilization is a steam flush-pressure pulsing process, which removes air rapidly by repeatedly alternating a steam flush and a pressure pulse above atmospheric pressure. Air is rapidly removed from the load as with the prevacuum sterilizer, but air leaks do not affect this process because the steam in the sterilizing chamber is always above atmospheric pressure. Typical sterilization temperatures and times are 132° C. to 135° C. with 3 to 4 minutes exposure time for porous loads and instruments.
Moist heat destroys microorganisms by the irreversible coagulation and denaturation of enzymes and structural proteins. In support of this fact, it has been found that the presence of moisture significantly affects the coagulation temperature of proteins and the temperature at which microorganisms are destroyed.
Steam sterilization should be used whenever possible on all critical and semicritical items that are heat and moisture resistant (e.g., steam sterilizable respiratory therapy and anesthesia equipment), even when not essential to prevent pathogen transmission. Steam sterilizers also are used in healthcare facilities to decontaminate microbiological waste and sharps containers but additional exposure time is required in the gravity displacement sterilizer for these items.
“Flash” steam sterilization was originally defined by Underwood and Perkins as sterilization of an unwrapped object at 132° C. for 3 minutes at 27-28 lbs. of pressure in a gravity displacement sterilizer.
Hydrogen peroxide is another agent used in disinfection and sterilization. Published reports ascribe good germicidal activity to hydrogen peroxide and attest to its bactericidal, virucidal, sporicidal, and fungicidal properties. Hydrogen peroxide works by producing destructive hydroxyl free radicals that can attack membrane lipids, DNA, and other essential cell components. Catalase, produced by aerobic organisms and facultative anaerobes that possess cytochrome systems, can protect cells from metabolically produced hydrogen peroxide by degrading hydrogen peroxide to water and oxygen. This defense is overwhelmed by the concentrations used for disinfection. Concentrations of hydrogen peroxide from 6% to 25% show promise as chemical sterilants. The product marketed as a sterilant is a premixed, ready-to-use chemical that contains 7.5% hydrogen peroxide and 0.85% phosphoric acid (to maintain a low pH). When the effectiveness of 7.5% hydrogen peroxide at 10 minutes was compared with 2% alkaline glutaraldehyde at 20 minutes in manual disinfection of endoscopes, no significant difference in germicidal activity was observed. A new, rapid-acting 13.4% hydrogen peroxide formulation (that is not yet FDA-cleared) has demonstrated sporicidal, mycobactericidal, fungicidal, and virucidal efficacy. Manufacturer data demonstrate that this solution sterilizes in 30 minutes and provides high-level disinfection in 5 minutes.